Abstract

Aims:

Melatonin has been reported to attenuate opioid tolerance. In this study, we explored the possible mechanism of melatonin in diminishing morphine tolerance.

Main methods:

Two intrathecal (i.t.) catheters were implanted in male Wistar rats for drug delivery. One was linked to a mini-osmotic pump for morphine or saline infusion. On the seventh day, 50 μg of melatonin or vehicle was injected through the other catheter instantly after discontinuation of morphine or saline infusion; 3 h later, 15 μg of morphine or saline was injected. The antinociceptive response was then measured using the tail-flick test every 30 min for 120 min.

The present study provides evidence that melatonin, acting via inhibiting morphine-induced neuroinflammation, can be useful as a therapeutic adjuvant for patients under long-term opioid treatment for pain relief.